Caption: Endoscopy. Doctor about to perform an endoscopic examination of a patient's stomach. This technique (gastroscopy) involves inserting the black, flexible, fibre-optic viewing tube down into the oesophagus, stomach and sometimes duodenum. At the end of the tube is a light that illuminates the inside of the body. The view from the end of the tube appears on a monitor (not seen). The technique is used to diagnose the cause of severe upper abdominal pain, or of blood in the vomit or faeces. It is also used to check for stomach ulcers or cancer.